Boat hull

ABSTRACT

A boat hull represented in a high speed attitude relative to a water surface-has a generally monohull section. A forward keel portion is flattened to form a plank-like planing surface having a replaceable shoe including stability extensions. Main bodies of sponsons are configured with air dams or spray walls. The sponsons define outer walls of side tunnels. The hull form, inboard of the side tunnels, provides side planing surfaces that step down transversely to the keel planing surface. Front and rear portions of the sponsons are connected by the air dam or spray walls and bound side tunnels having side planks or planing surfaces disposed at their inner edge. A step in the keel is provided to define a tunnel disposed between two downwardly depending side walls. Across afterplanes an integrated undersurface has an outboard motor insertion space with a continuation of the recess upper surface and provides a lateral boundary of a space. In use at speed, the planing surface supporting a bulk of a weight of the vessel includes a region including elements of the keel planing surface, portions of the main hull and side planing surfaces, with additional support and lift being generated by outer sponson contact areas.

This invention relates to a boat hull.

TECHNICAL FIELD

This invention has particular but not exclusive application to outboardmotor powered monohull planing boat hulls, and for illustrative purposesreference will be made to such application. However, it is to beunderstood that this invention could be used in other applications, suchas multihull vessels, seaplane floats or the like, inboard poweredplaning vessels, inboard outboard powered planing vessels, jet poweredboats including personal jet skis (personal water craft) and airboats.

BACKGROUND OF INVENTION

In general, outboard motor powered boats have evolved from hull shapesgenerally designed for inboard power. Such hulls generally include abottom part including a keel extending from stem to transom, the keeland its immediate surrounds providing a planing surface at speed. Onedisadvantage of this traditional type of planing hull is the disruptionof the water behind the planing surface, which leads to propellerinefficiency. Of course, in single motor applications with monohulls, itis generally unavoidable that the planing surface precede the propelleralong the centreline of the hull.

It has been proposed to partially overcome the disadvantages oftraditional hull design by use of an extended transom or pod. However,the extended transom or pod places the weight of the outboardsignificantly behind the normal position relative to both the centre ofgravity of the assembled rig and the planing surface at speed,disturbing the balance of the boat. This problem is exacerbated with thenew heavier 4 stroke outboards becoming popular around the world.

As an improvement in the traditional planing hull and avoiding thedisadvantage of pods or extended transoms, it has been proposed to stepthe transom to the keel of the hull to separate the keel from thepropeller. In general such stepped designs include the underside of thestep as part of the planing surface or at least part of the bearingsurface under displacing conditions. Accordingly, such surfaces aregenerally provided with strakes and other interactive protuberances.Australian Patent Application No. 17654/88 (Haines 1988) discloses ahull having a transverse step of generally horizontal disposition andextending from the transom for approximately 5 to 15% of the waterlinelength of the hull ahead of the transom. It has been found that thedisclosed apparatus when planing interacts with the surface 17 as muchas the keel 11, generating spray and turbulence ahead of the propeller,and thus providing a source of inefficiency.

U.S. Pat. No. 1,396,831 (Gardner 1921) discloses a hull having a hullrelieved by a cavity, the side walls of the cavity being configured torake directly aft from the keel step to the transom and the recessdefined thereby opens out essentially across the full width of thetransom. The rake angle of the side walls, diverging sharply from thestep, introduces cavitation in the turns. That this appears to have beenan inherent problem with the apparatus disclosed in the cited referencebecomes apparent when it is observed that the propeller is shown verylow in the water. The decreased buoyancy of the aft portion of thevessel brought about by the substantially full-width transom openingresults in the transom opening of the recess being fully submerged, andis thus not vented through the transom to assist initial release. Thedisclosure will also, by virtue of the limited lift aft and smallplaning surface area at the transom, be prone to porpoising untilplaning at high speed. Given the long length of the recess, this wouldhave further increased the cavitation tendency mentioned earlier. FIG. 1of the reference illustrates an apparatus wherein the top surface of therecess is minimally above the water line at rest. At low speed thecavity would be fully submerged as the application of power tended todrive the stern downward.

Similarly, reference DE 410034 (Bonnemaison 1925) discloses apparatushaving a recess which is triangular and thus has all of thedisadvantages inherent in the Gardner apparatus. The recess is almostfull length and again it is full width at the transom. With the verysmall planing surface area near the transom, the present applicantdoubts that the design would work and if it were to be operable at all,very large levels of power would be required to get it planing and itwould be very prone to porpoising at low planing speeds.

With reference to U.S. Pat. No. 1,831,339 (Brush 1931), this disclosesapparatus including a recess which is parallel sided and transverse tothe boat at the front, like that referred to Australian patentapplication No 17654/88 (Haines 1988). The step extends for the fullwidth of the hull and thus does not have stability in turns, since thedownwardly depending side portions are substantially absent for aconsiderable distance aft of the step. The aft planing surfaces at eachside of the hull are substantially flat and high lifting, preventingvessel trimming at speed. The disclosed apparatus uses a complex bottomin an attempt to have all 3 water contact points separated, and in thisrespect the disclosed apparatus is directed to effectively a planingmultihull or foil borne apparatus rather than a planing monohull. Theseparation of the planing surfaces appears to be driven by a belief thatall parts of the boat should operate in undisturbed water. This wouldgreatly add to the manufacturing costs and because each of the rearplaning surfaces is essentially horizontal, it will give excess spray infront of the propeller and so cause cavitation like the apparatusdisclosed in 17654/88.

With reference to U.S. Pat. No. 3,547,064 (Glass 1968), the disclosedapparatus has a recess that is triangular and full width with theattendant disadvantages described above. The cited disclosure describesa hull adapted to touch the water at the transom immediately in front ofthe propeller when on the plane. The disclosed apparatus thus lacks theadvantage of AU668684 of minimising the water disturbance in front ofthe propeller.

As the transom is not open, venting internally is necessary until theboat runs at very high speed. The disclosed apparatus has two deltashaped contact points with the water. As a result of the transom contactand the full width step, the venting is complex and therefore expensive.Because of the relatively small contact area at the transom, theapplicant would expect that the disclosed boat, like the Gardner and theBonnemaison designs, would be very prone to porpoising until running atvery high planing speeds. The disclosure of the reference is express, atpage 2, line 60, that the rear recessed section should be parallel withthe front planing section. Page 4, line 3 of the disclosure also statesan aim of trying to develop an air cushion requiring complicated ventingand an attempt to introduce ram air.

WO 89/02846 (Monocat Powerboats) discloses apparatus having a catamaranform aft for planing With a deep-V form forward for sea keepingqualities. The disclosed apparatus is borne on three points. The tunnelshape is not a shape consistent with efficiently getting the boat on theplane or allowing the propeller (or propellers in the case of twin motorapplications) to be mounted high and therefore to decrease the boatdraft. The drawings of the reference show high speed ocean type raceboats where these attributes would have not been important. Theapparatus does not disclose placing the propellers behind the tunnelbecause the water there will be very disturbed because of the divergentshape of the tunnel. This design therefore will not achieve theobjective of having relatively undisturbed water in front of thepropeller and so increase the propeller efficiency. The drawings of thecited reference show the propellers behind the deep vee and this is onlyacceptable in race style boats using very expensive surface chopperpropellers.

Australian Patent 668684 discloses a boat hull of the stepped typeincluding a keel having a single planing surface adapted tosubstantially support the hull at planing speeds. The hull has adownwardly depending hull side portion disposed on each side of the keeland extending aft to a transom, and an upper substantially plane surfaceextending rearward from the step of said keel. The step and sideportions and upper surface define a recess opening through and extendingforward from the transom to the step. The recess extends for asubstantial part of the waterline length of the hull and configured suchthat the upper surface at planing speeds is substantially clear of thewater, the recess being provided with vent means to vent the recess toatmosphere as the hull approaches planing speed.

The boat hull described minimizes disturbance in front of the propellerand thus permits the propeller to operate in water substantiallyundisrupted by the keel of the hull. However, there has in someembodiments been the tendency to porpoising.

The present invention aims (when applied to a monohull) to provide theride, handling and directional stability of a deep vee monohull, butwith the speed, low wake, shallow draft and lateral stability of a flatbottom boat. It should also contain the spray to improve ride and speedand to decrease the water spray into the boat in windy conditions. Itshould also substantially alleviate the problem of disturbed waterentering the propeller area which is one of the principal disadvantagesof conventional boat hulls and the present invention further aims toprovide an improvement over current stepped transom designs and thedesign of AU 668684, and to provide a boat hull which will be reliableand efficient in use. Other objects and advantages of this inventionwill hereinafter become apparent.

SUMMARY OF THE INVENTION

With the foregoing and other objects in view, this invention in oneaspect resides broadly in a boat hull including:

a forward keel portion having a forward planing surface formed thereon;

a recess opening through and extending forward from a transom of thehull and meeting said keel at a step, said recess having an uppersurface extending rearward from said step and opposed downwardlydepending side walls;

a pair of aft planing surfaces each formed-adjacent to and outboard of arespective one of said side walls and extending aft from the region ofsaid step; and

a pair of sponsons each formed outboard of a respective one of said aftplaning surfaces.

The hull may be of any suitable type including monohulls and multihulls.Where a multihull or power cat type hull is required, a recess may beprovided for each hull or keel or alternatively the recess may extendacross both keels.

Preferably, the recess relieves the keel forward of the transom for atleast 25% of the waterline length of the boat at planing speeds, with itbeing particularly preferred that the recess relieve the keel ahead ofthe transom for at least 40% of the planing waterline length. Typically,relief of the keel for 40% of the waterline length on the plane willamount to approximately 25% of the waterline length under displacingconditions. For typical deep-V type hulls, such criteria will translateto a recess length of at least 20% of the overall length, depending onthe gross weight, speed and deadrise angle of the hull.

Preferably, the recess is configured such that at planing speeds theupper surface of the recess is substantially clear of the water surface.This provides for relatively uninterrupted water for the propeller, aswell as decreasing the wetted area of the hull on the plane. Aperformance improvement, thought to be caused by the decreased wettedsurface area when the boat is driven above planing speed, is noticeablewhen the upper surface of the recess comes clear of the water.

A further performance gain appears to be obtained by the aforesaidrelatively undisturbed water in front of the propeller, in a mannerthought to be analogous to that achieved with an extended transom orpod. In this area the advantage over a pod is that the distance betweenwhere the boat touches the water in front of the propeller and thepropeller itself is increased significantly over that of the traditionalhull, without disturbing the balance of the boat.

In order to facilitate the desired clearance without an excessive stepit is preferred that the forward part of the upper surface of the recessbe inclined rearward and upwards from the step. Preferably, theinclination of the forward part of the upper surface is selected suchthat the upper recess surface at planing speeds is at least parallel toand clear of the water. Of course, the surface may be more inclined thanis necessary, and the rear portion of the upper surface will beapproximately parallel to the keel to allow the same effective angle ofattack when this surface is touching the water at low speeds. In atypical application, an inclination such as that described by a recesshaving a depth approximating 20% of the length of the forward slopingportion of the recess has been found to be adequate for typical planinghulls, although this will of course depend on the gross weight, speed,deadrise angle and planing angle of a particular hull.

The recess may be vented to the top of the hull or to the side to assistin breaking the suction of the upper surface of the recess to the wateras the recess comes clear of the water. In some high speed applications,the upper surface of the recess may be so configured as to clear thewater surface at a selected speed above the lowest planing speed. Thevent allows the false bottom defined by the top surface of the recess tobe released at a lower speed than it otherwise would but once releasedit is believed that the vent has no further significant effect.Alternatively, the opening of the recess through the transom may affectthe venting as the vessel gains speed.

Preferably, the upper surface of the recess is a plane surface to avoidinadvertent interaction with the water surface in the planing condition,although the surface may be provided with reinforcing or ribs wherethese are deemed necessary to provide adequate strength or stability.Where such reinforcing or ribs are necessary, these may be providedwithin the hull rather than disturb the recessed upper surface.

The lower edges of the side walls bounding the recess may also beprovided with spray rails, strakes or other means of engaging the watersurface at planing speeds to increase lateral stability. These may takethe form of bounding the recess at its sides by downwardly dependinghull side portions, the hull side portions providing greater length ofwater contact in turns than when the hull is moving straight ahead. Thisprovides a desirable increase in lateral stability in the turns bymaximizing the length of the effective “keel” in the turns. Lateralstability limitations have been found to be a disadvantage of apparatussuch as that disclosed in Australian Patent No. 585713 (Haines 1987)which proposes a full width transverse step, in embodiments wherelight-construction boats are provided with relatively large outboardmotors. Such spray rails, strakes or other means of engaging the watersurface at planing speeds are preferably parallel to the centerline topromote turn stability without increasing drag and spray generation.

The sponsons of the present invention may be selected in form such thatat rest or at displacement speeds the length of the hull in the water ismaximized to improve ride and stability whilst allowing the boat toplane at very low speeds. The sponsons are substantially lifted clear toprovide a small contact area with the water at higher planing speeds. Ifdesired, a degree of after planing surface may be provided towards therear of the sponsons. The sponsons may incorporate a longitudinallydisposed, generally downward depending air dam or spray wall. It hasbeen found that such spray walls contain the spray and water which isejected out the side and the rear of a typical mono or multi hulled boatas this represents wasted energy and causes the occupants of the boat tobe wet in any more than light cross winds. Containing the spray andwater also has been surprisingly determined to improve the ride of thehull at planing speeds. Trapping the spray and air also decreases thefriction against the hull as aerated water has been shown to produceless drag than normal water. As well as increasing speed, this allowsthe boat to plane at lower speeds than either a conventional boat or theone described in AU 668684.

The spray walls may extend behind the aft planing surfaces to hold thespray away from the motor leg area. In embodiments utilizingafterplanes, such spray walls may be configured to keep the majority ofthe spray under and behind the after planes. Allowing spray into themotor leg area would increase motor corrosion (an accepted major problemin catamarans) and decrease the “lubricating effects of the spray” whilethe afterplanes are touching the water.

The configuration of the present hull serves to decrease the draft ofthe boat and to allow the motor to be mounted high and so allowoperation in shallow water. This was also a characteristic of AU 668684,but the present invention allows the motor to be mounted even higher andfor the boat to draw even less water at speed. The provision of aplaning surface which extends to the rear of the step vis the aftplaning surfaces and optionally the sponson aft planing surface allowsthe hull to run at almost constant angle (angle of attack to the water)regardless of the speed of the boat. This particularly applies when theboat is approaching planing speed, where the hull meets the resistanceknown as “getting over the hump”. This reduction in bow up tendency alsodecreases the wake and the visibility and stability problems well knownwhen a boat is operating around minimum planing speed. The contact areasat planing speeds also may have a constant angle of attack to improveefficiency and decrease the tendency for the boat to porpoise or rocksideways particularly in rough water, or may be configured to havediffering angles of attack, depending on the overall hull form andgeometry. Most monohull boats have a much lower angle of attack at thekeel than at the chine as a consequence of the vee becoming deepertowards the bow. Having a constant angle of attack over the length andwidth of the boat allows the angle of attack to be more easily optimizedin the “tuning” process.

The planing surfaces of the hull may be provided with a replaceableshoe, especially the keel planing surface, which is designed to be openover much of the forward part of lower surface and with a very sharpangle of entry to minimize forces when this area of the hull “slaps”into the water. The forward part of the shoe also traps air and sofurther minimizes hull “slapping” onto the water in rough waterconditions. It is envisaged that the forward section of the keelreplaceable shoe would be suitable for installation as an after marketitem on any mono, cat or multi hull. This shoe is of maximum benefit inimproving the ride when it is fitted to a boat which operates at speedssuch that the forward section of the keel is above the water whenoperating in smooth water. The replaceable shoes on all planing surfacesprovides the ability to “tune” the boat to the preferred operatingconditions and to replace the shoe when it is damaged. The shoes arepreferably of a more durable material than the aluminium or glasscomposite preferred for the hull proper, such as stainless steel or somegood wearing reinforced plastic or composite material. The shoe ispreferably designed so it is easily removable with bolting or cutting.Insofar as other planing surfaces such as the side plank planingsurface, the aft planing surfaces and sponson planing surfaces areconcerned, these may be selectable as to form to provide the ability totune the length and the width of the main and side planks to change theamount of lift generated near the transom of the boat and to change thecentre of lift without major modifications to the overall boat hull.Spacers are frequently placed between motors and the transom to tune theboat by moving the centre of gravity of the boat further aft (by movingthe motor further aft) and so introduce more bow lift at high speeds.Decreasing the overall length of the side planks at the transom end willallow the same effect in the present invention.

A useful effect of the hull forms of the present invention is to providefor a boat shape with deep section shape changes across the boat and soallow good strength in bending in the fore and aft direction regardlessof whether it is constructed out of metal, wood or fibre reinforcedplastic or composite.

One or more of the surfaces of the underside of the hull at the transommay be extended aft about the motor mounting in the form of afterplanes.The afterplanes disclosed in this specification may be constructed asplaning surfaces or may be constructed with flotation having a planingundersurface. The use of afterplane flotation increases safety andstability in both fore and aft and lateral directions and provides aconvenient access point onto the boat. The floatation in the afterplanesalso decreases the tendency of the transom of the boat to bury deep intothe water when being loaded onto or off trailers. This is very importantin both shallow water and when loading or unloading the boat in roughwater conditions e.g. launching in the sea. This flotation at thetransom also allows the trailer to be almost completely out of the waterwhile launching and retrieving the boat and this decreases the corrosionof the trailer, particularly in salt water.

The recess in front of the transom may mount external sensors andequipment which ordinarily would be mounted in an exposed position or atthe transom. For example, an echo sounder transducer, water temp sensorand paddle wheel or petot tube speedometer may be mounted well forwardin the boat without the complication of mounting the sensors through thehull. The cables may then be brought to the inside of the boat throughthe optional vents for the recess, or through grommets provided in thisarea, which would not require over rigorous sealing or watertightness.Water pickups (for example for live bait tanks) can be installed in thecentral recess and so provide “run aground” protection therefore.

The aft planing surfaces and optional sponson planing surfaces may besuch that the keel planing surface is lifted so it is above the water atvery high speed and so make the boat essentially like a tunnel hull orhydroplane at high speed and a mono at low planing speed. In theextreme, this would allow the pointed bow to be removed where decreasedlength was of benefit for example smooth water work and the boat wouldthen essentially become a Catamaran or a Hydroplane with a complex shapein each sponson.

The afterplane may be fixed afterplanes, but an adjustable section inthe form of trim tabs can be incorporated if side to side weight balanceor additional for and aft adjustments are desired. The tabs may beincorporated at the rear end of the afterplanes, well behind the transomor alternatively at the rear end of the aft planing surfaces i.e. thefront portion of the afterplanes or in front of the transom. If lengthreduction or weight reduction is important, the afterplanes could bedeleted or size decreased and their effect decreased. Since theafterplanes are essentially out of the water at high speed, only smallversions if any would be fitted to smooth water race boats.

Hulls having afterplanes in accordance with the present invention act asif the transom were stepped and so allow the rear contact point of thewater to be adjustable (compared with the centre of gravity of the boat)by either extending or shortening the aft planing surfaces. This may beadvantageous in getting the boat to have a good positive angle of attackat high speed as the tendency of a non stepped boat is to decrease theangle of attack as the speed increases and this is what causes highspeed boats to need to run extreme out trim on the leg of the motor athigh speed.

Apparatus in accordance with the present invention uses the sameprinciple of minimizing disturbance in front of the propeller, comparedwith the hulls of AU 668684, but increases the length of the steppedcentral section and utilizes a boat design with a formed planing surface(flat plank) instead of a vee shape at the keel as described in theearlier patents. A vee shape at the keel can still be utilized With thisdesign for simplicity, or improved ride if they were determining factorsin the selection of the keel shape. When a flat plank keel is used, theforward section of the embodiment described in the earlier patent is nowat right angles to the direction of travel. Air is also trapped underthe hull, except in the recess, to improve ride and increase speed. Athigh speeds all of the afterplanes and most of the side sponsons are outof the water to minimize drag and so maximize speed. The detailed shapeof the afterplanes and the speed at which they are completely above thewater can be adjusted by the height and distance each part of theafterplane is behind the section of the hull ahead of the afterplane.This relationship between the hull and the afterplane can also be usedto control the angle of attack of the boat at all operating speeds andthe degree of banking of the hull in turns, both above and below planingspeeds.

BRIEF DESCRIPTION OF DRAWINGS

In order that this invention may be more easily understood and put intopractical effect, reference will now be made to the accompanyingdrawings which illustrate a preferred embodiment of the invention,wherein:

FIG. 1 is a side elevation of a boat hull in accordance with the presentinvention;

FIG. 2 is a plan view of the boat hull of FIG. 1 illustrating criticalhull contact surfaces;

FIGS. 3 to 6 are transverse sections designated A—A to D—D through thehull of FIGS. 1 and 2, and

FIG. 7 is an alternative section D—D.

DETAILED DESCRIPTION

In the Figures there is generally illustrated by the numeral 10 a boathull in accordance with the present invention and represented in a highspeed attitude relative to a water surface 11. The technical details ofthe hull 10 insofar as its active surfaces and configuration areconcerned are illustrated most clearly in the plan view of FIG. 2 andthe transverse sections of FIGS. 3 to 7.

In the plan view of FIG. 2, and moving aft from the bow end of the chineline 12, there is provided a generally monohull section 13 asillustrated in FIG. 3 corresponding to section line AA of FIG. 1. Inthis section, the forward keel portion 14 is flattened to form aplank-like planing surface 15. In the embodiment illustrated, the keelplaning surface 15 is provided by means of a replaceable shoe includingstability extensions 16. At the section AA illustrated in FIG. 3, theforward vestiges of sponsons 17 and side planing surfaces 18 can beseen. A foredeck plan line 20 is also illustrated in FIG. 2.

At the section BB illustrated in FIG. 4, the transition from therelatively conventional monohull section of FIG. 3 commences with theintroduction of the main body of the sponsons 17 which are configuredwith air dams or spray walls 21, the sponsons 17 defining the outer wallof side tunnels 22. The hull form inboard of the side tunnels 22 isconfigured with the forward end of side planing surfaces 23 andthereafter steps down to the keel planing surface 15.

Proceeding further aft, in FIG. 5 the section CC illustrates the hull 10wherein the section continues aft with the rear portion of the sponsons17 and aft sections of their planing surfaces 24, the front and rearportions of the sponsons being connected by the aforementioned air damor spray walls 21, again bounding the side tunnels 22 having the sideplanks or planing surfaces 23 disposed at their inner edge. Thedifference in this section is the provision of a step in the keel todefine a tunnel 25 disposed between two downwardly depending side walls26.

In the section DD, this is taken across after planes 27 and illustratingan integrated undersurface having an outboard motor insertion space 28with a continuation of the recess upper surface 30 providing the lateralboundary of the space 28. The side tunnels 22 are generally continuedinto the after plane 27 as side tunnel extension 31 having an uppersurface generally higher than the upper surface of the side tunnels 22,in this embodiment.

In the alternative after plane section of FIG. 7, the features aregenerally numbered as per FIG. 6, however in this embodiment, the sidetunnel extensions 31 are relieved out at 32 to flatten the after planesection.

In use at speed, best illustrated in FIG. 2, the planing surfacesupporting the bulk of the weight of the vessel comprises the stippledregion 33 comprising elements of the keel planing surface 15, portionsof the main hull 10 and side planing surfaces 18, with additionalsupport and lift being generated by similarly stippled outer sponsoncontact areas 34.

The elevation of FIG. 1 shows a side view of the boat including thestepped side sponsons, stepped plank style keel and the afterplane. Theheight of the steps and the relationship of this to the distance betweensteps has a significant impact on the angle of attack of the boatparticularly at high speed. The angle of attack is shown with thehorizontal line towards the front of the boat representing water levelat high speed. The stepped planked keel is arranged to trap air when inrough water and so minimize rough ride.

The shape of this is shown in more detail in Section AA (FIG. 3), andare referred to as stability extensions of the plank in the bow area.

For some applications, there may be more or less than the 2 sponson and1 keel steps shown in this design. The surface of each sponson touchingthe water is essentially horizontal laterally and parallel to the keelline of the boat. For some applications for example skiing where tightturning is required, some lift could be compromised and the sponsonsmade to slope upwards to the outside of the boat. Also the height of thesponsons could be arranged to be above the water at very high speed,whilst still retaining the value of the sponson arrangement described atlower operating speeds and while stationary.

FIG. 2 shows a plan view of the hull with the stippled area indicatingthe contact with the water at high speed. The central recess (or tunnel)covered by the earlier patent AU 668684 is clearly visible and thisresults in a relatively long water contact zone with a small surfacearea. FIG. 2 also shows the locations for vents 35 into the centraltunnel and behind the side planks; 36 shows the alternative positionsfor trim tabs where fitted and 37 shows the alternative positions forsensors to cover speed temperature and echo sounder transducer in areasprotected from damage. This sketch does not show the air dams or spraywalls between the sponson steps to minimize the energy loss, trap air toimprove ride and decrease spray to the outside of the boat. These airdams are however shown in Sections BB and CC (FIGS. 4 and 5). It alsodoes not show the sloping walls along the side of bow section of thekeel plank which trap air to minimize the slapping of the plank on roughwater and so causing vertical accelerations which in turn cause a roughride. These sloping walls 16 are however shown in Section AA. Theseextensions of the plank in the bow area is a feature which caneffectively be fitted to conventional boats regardless of whether or notthey are fitted with vee or plank shaped keels. For cost reductions orsimplicity, either or both the spray walls may not be fitted in someapplications. In some applications for example rough water, it may bebeneficial to increase the waterline length of the boat and this can bedone by having the rear end of the afterplanes still touching the watereven at high speed. The waterline length at high speed will also beincreased by the extensions of the plank in the bow area and increasingthe depth of the keel steps will further increase the waterline length.

The angle of attack of the boat (trim angle) can be tuned at both lowand high speeds by adjusting the height and the location of the steps;i.e. moving the rear end of the side sponson or the side plank or both,forwards, will increase the angle of attack at high speed and havevirtually no effect on the angle of attack at lower speeds. This tuningis in addition to that normally done with fore to aft weightdistribution, use of trim tabs and motor (or leg) trim angle.

The trim angle at lower planing speeds can be adjusted by increasing theheight of the rear end of the front section of the side sponson as thiscreates significant lift at lower speeds, but is intended to be clear ofwater at high speed so has no effect on high speed angle of attack.

The trim angle at displacement speed can be changed by alterations tothe surface area of the afterplanes and the displacement volume of theafterplanes. Since these don't touch the water at high speed, they alsohave no effect on high speed angle of attack. The plan view does notshow the replacement shoe covering the plank surface which could includethe sloping walls on the side of the plank referred to in an earlierparagraph. This replacement shoe, would be the first part of the boat totouch debris or ground, and its fitment would allow this to be made frommore durable material than the majority of the boat hull. It also allowsthe shape of the shoe to be tailored to specific requirements e.g. goodride at the expense of speed. This replaceable shoe also incorporatesthe sloping walls referred to above. The replaceable shoe is not arequirement of the design and for simplicity and or cost reductions,this may not be fitted in some applications.

Section AA (FIG. 3) shows the cross section of the hull at the front endof the front sponson at Section AA as shown in the Elevation. Note thatall lines shown as straight in all cross sections could be curved tosimplify construction, to improve handling, to improve ride or improvestrength in certain applications.

Section BB (FIG. 4) shows the section of the hull across the frontsponson but in front of the tunnel.

Section CC (FIG. 5) is a section across the rear sponson and across thetunnel of the hull.

These sketches show a central planing plank, but it is not required forthe design. If the plank was deleted, the tunnel shape would be exactlythat shown in earlier patent AU 668684.

Section DD (FIGS. 6 & 7) shows two alternative sections of the forwardsection of the afterplanes. The central part of both sections are shownat the same height as the recess (tunnel) in front of it. In someapplications, this may not be at the same height and the afterplane maynot be flat in the central part as shown in this figure. The after planeside tunnel extension may be of the same height as the side tunnel topsurface, or may be higher than it.

In the preferred embodiments the section shapes provide air access atboth low and at high speeds so there is no venting required except forbehind the rear section of the side planks and the central recess(tunnel) as discussed in earlier patent AU 668684.

The air trapped under the hull is a function of the square of the speedand this trapped air increases the speed for any level of power and alsoimproves the ride by partially supporting the hull on a cushion of air.This is more noticeable at high speed and in some applications, it isbeneficial to increase the tendency to trap air under the hull. This canbe done by extending the walls (air dams) associated with the sponsonsfurther forward and also by adding walls under the afterplanes, behindthe side planks as this decreases the tendency to allow air to escapeinto the rear section of the recess and the front central section of theafterplanes. Further walls can be added under the afterplanes and behindthe sponsons to stop the loss of air and spray out the sides of the boatin the afterplane area. To maximize the efficiency of the air dams, itis expected that they will generally be out of the water at high speedto minimize drag and for the bottom surfaces to be parallel to the waterto minimize the air losses at speed.

It will of course be realised that while the above has been given by wayof illustrative example of this invention, all such and othermodifications and variations thereto as would be apparent to personsskilled in the art are deemed to fall within the broad scope and ambitof this invention as defined in the claims appended hereto.

What is claimed is:
 1. A boat having a hull, the hull comprising: a keelhaving a forward keel portion having a forward planing surface formedthereon; a recess opening through and extending forward from a transomof the hull and meeting said keel at a step, said recess having an uppersubstantially plane surface extending rearward from said step andopposed downwardly depending side walls, the upper surface configured tobe essentially clear of a water at planing speeds; a pair of aft planingsurfaces each formed adjacent to and outboard of a respective one ofsaid side walls and extending aft from the region of said step; and apair of sponsons each formed outboard of a respective one of said aftplaning surfaces.
 2. A boat hull according to claim 1, wherein therecess relieves the keel forward of the transom for at least 25% of awaterline length of the boat at planing speeds.
 3. A boat hull accordingto claim 2, wherein said recess relieves the keel ahead of the transomfor at least 40% of the planing waterline length.
 4. A boat hullaccording to claim 1, wherein a forward part of said upper surface ofthe recess is inclined rearward and upwards from the step.
 5. A boathull according to claim 4, wherein said inclination of the forward partof the upper surface is selected such that the upper surface of therecess at planing speeds is at least parallel to and clear of the water.6. A boat hull according to claim 1, wherein said recess is vented to atop of the hull or to a side to assist in breaking a suction between theupper surface of the recess to the water as the recess comes clear ofthe water.
 7. A boat hull according to claim 1, wherein lower edges ofthe side walls bounding the recess are provided with lateral stabilizingmeans selected from spray rails, strakes, air dams and other additionsused to limit the flow of water, air or spray into the recess.
 8. A boathull according to claim 7, wherein the side walls bounding the recess atits sides comprise downwardly depending hull side portions, the hullside portions having minimal contact with the water when the hull ismoving straight ahead, and provide greater length of water contact inturns.
 9. A boat hull according to claim 1, wherein said sponsons areselected in form such that at rest or at displacement speeds a length ofthe hull in the water is maximized to improve ride and stability whilstallowing the boat to plane at very low speeds.
 10. A boat hull accordingto claim 9, wherein said sponsons are substantially lifted clear toprovide a small contact area with the water at higher planing speeds.11. A boat hull according to claim 1, wherein a degree of after planingsurface is provided towards a rear of the sponsons.
 12. A boat hullaccording to claim 1, wherein said sponsons incorporate a longitudinallydisposed, generally downward depending air dam or spray wall.
 13. A boathull according to claim 1, wherein one or more of the planing surfacesof the hull are provided with a replaceable shoe.
 14. A boat hullaccording to claim 13, wherein said at least one planing surfacecomprises a keel planing surface.
 15. A boat hull according to claim 13,wherein said planing surfaces are selectable as to form to provide theability to tune the length and the width of the surfaces to change theamount of lift generated near the transom of the boat and to change acenter of lift without major modifications to the overall boat hull. 16.A boat hull according to claim 1, wherein the keel is fitted with areplaceable shoe of a configuration selected to improve a ride andhandling of the boat and also be suitable for installation as an aftermarket item on an existing monohull, catamaran or multi hull vessel. 17.A boat hull according claim 1, wherein one or more of the surfaces ofthe underside of the hull at the transom are extended aft about a motormounting in the form of afterplanes.
 18. A boat hull according to claim17, wherein said afterplanes are selected from planing surfaces andflotation having a planing undersurface, the planing surfaces beingsubstantially parallel to the keel and configured to be substantiallyclear of the water at high speeds.
 19. A boat hull according to claim18, wherein said afterplanes comprise trim tabs whereby side to sideweight balance and/or additional fore and aft adjustments is provided.20. A boat hull according to claim 19, wherein said trim tabs areincorporated at a position selected from the rear end of the afterplanesand the rear end of the aft planing surfaces at a front portion of theafterplanes.
 21. A boat hull according to claim 17 wherein saidafterplanes are essentially above water at high operating speeds.
 22. Aboat hull according to claim 1, wherein said recess in front of thetransom mounts external sensors and equipment which ordinarily would bemounted in an exposed position or at the transom.
 23. A boat hullaccording to claim 1, wherein the aft planing surfaces and planingsurfaces provided on the sponsons are such that the keel planing surfaceis lifted so it is above the water at very high speed and so make theboat essentially like a tunnel hull or hydroplane at high speed and amonohull at low planing speed.